add read only tree table and value help

bookshop/db/schema.cds

@@ -25,7 +25,7 @@ entity Authors : managed {
 
 /** Hierarchically organized Code List for Genres */
 entity Genres : sap.common.CodeList {
-  key ID   : Integer;
+  key ID   : UUID;
   parent   : Association to Genres;
   children : Composition of many Genres on children.parent = $self;
 }